In a personal computer (PC) such as a desktop PC, a laptop PC, a tablet terminal and so forth, many electronic devices such as a CPU, a GPU, a chipset, an input/output device and so forth are packaged in the chassis at a high density. These electronic devices generate heat in accordance with an operation of the PC and rising temperatures of the electronic devices and the chassis. The PC which is requested to have comparatively high processing ability is provided with a heat radiation fan which performs control by using temperature sensors disposed in chips of main electronic devices or on a surface of the chassis for management of the temperatures of the electronic devices and the chassis.
When a measured temperature by the temperature sensor rises, the heat radiation fan replaces air in the chassis with outer air. The temperature is determined depending on the heat generation amount of the electronic devices and a heat radiation amount of the heat radiation fan. The heat radiation fan is able to adjust the heat radiation amount by controlling a rotational speed thereof to a plurality of steps. The rotational speed of the heat radiation fan is controlled to increase when the measured temperature by the temperature sensor exceeds a threshold value and to decrease when the measured temperature becomes lower than the threshold value. The CPU generates the largest heat amount in the electronic devices loaded on the PC.
The heat generation amount of the CPU is determined by power consumption. There is known a technique called SpeedStep (a registered trademark) for lowering the power consumption by lowering a clock speed and an operating voltage of the CPU. Further, there is also known a technique called Throttling for intermittently operating the CPU in order to lower the power consumption. It is possible to lower the heat generation amount by lowering the processing ability of the CPU by both of these techniques.
In addition, in the specification of ACPI (Advanced Configuration and Power Interface), two systems, that is, an active cleaning system and a passive cleaning system are defined for heat radiation of a computer system. In the active cleaning system, when the temperature of the computer begins to rise, the heat radiation fan is operated first and then in a case where the temperature keeps rising even when the rotational speed of the heat radiation fan reaches a maximum value, the processing ability of the CPU is lowered.
In the passive cleaning system, when the temperature of the computer begins to rise, the processing ability of the CPU is lowered first and then in a case where the temperature keeps rising even when the processing ability of the CPU is lowered to a lowest level, the heat radiation fan is operated. The active cleaning system is based on a way of thinking that the processing ability is preferred and the passive cleaning system is based on a way of thinking that an increase in power consumption and suppression of noise of the heat radiation fan are preferred.
Patent Document 1 discloses a heat radiation system which gives maximum amenity to a user by harmonizing the processing ability of the processor with the noise generated by rotation of the heat radiation fan. In Patent Document 1, it is described that when it is anticipated that the temperature sensor detects that a measured temperature would exceed a threshold value on the basis of which the rotational speed of the heat radiation fan is raised by one step in a predetermined time, the processing ability of the processor is temporarily lowered and work which is not executed is shifted to a light-load time zone so as not to raise the rotational speed of the heat radiation fan.
Patent Document 2 discloses the invention of dynamically making a switch between the active cleaning system of rotating a cooling fan first by preferring retention of the processing ability of the CPU and the passive cleaning system of lowering the processing ability of the CPU by preferring suppression of the rotational speed of the cooling fan when the temperature of the personal computer rises. In Patent Document 2, it is described that the cleaning system is switched by triggering the kind of a power source used, an opened/closed state of a display panel and so forth.
Patent Document 3 discloses the invention of preventing generation of unnecessary noise caused by a rising rotational speed of the cooling fan that the laptop PC loads. In Patent Document 3, it is described that when the electronic devices such as the CPU, a video chip and so forth are in idle states, rising of the rotational speed of the cooling fan by a temperature sensor which monitors the electronic device concerned is suppressed on the basis of heat radiated from other electronic devices.
Patent Document 4 discloses a portable computer which is provided with two cooling functions, that is, the function of lowering an operating speed of the CPU and the function of rotating an electric fan. In Patent Document 4, it is described that in a case where a user selects a Quiet mode, the electric fan is not operated and only the operating speed of the CPU is lowered and in a case where the user selects a Performance mode, the computer enters a performance preference mode and cooling is performed only by rotation of the electric fan without lowering the operating speed of the CPU.